It was a shame that Mishima could not accept who he was. This instability helped fuel his creativity. However, it arguably contributed to him believing in the most reactionary form of politics. As a consequence, he was involved in a coup attempt. He could never accept democracy. When his political disappointment was acute, he killed himself.
The problem for Mishima was thus personal and political. He could never address the tensions and contradictions that marked so much of his life. However, he was an individual in society and it would be wrong to put everything on his shoulders. He was not to blame for the way he was socialised.
Amid all this, it is perhaps sensible to remember that the writer was not reducible to his flaws. If one puts aside his misguided admiration for violence, he was a poet who tried to express something about the human condition.